Infrared (IR) imaging has increasingly been used in the preventative maintenance of high voltage electrical circuits and components. An IR image of the components can often reveal hot spots which may indicate malfunctioning, improperly connected, or overloaded components. Timely identification of problem components can save on system downtime and expenses associated with replacing blown or destroyed components.
To effectively inspect electrical components, a thermographer should view the components with an IR camera while the components are operating or energized. However, this can be difficult because electrical components are often kept in high voltage electrical cabinets. Because an IR camera requires a line of sight to deliver a suitably accurate thermal image, components within a cabinet cannot be imaged adequately without either opening the cabinet or providing some other view into the cabinet.
Opening a high voltage electrical cabinet while the components within are energized poses a risk of arc flashing. To avoid this risk, most cabinets include door interlocks which require that the components within be powered off before the cabinet can be opened. But when the power is turned off the components within the cabinet begin to cool and heat within the cabinet is rapidly dissipated or redistributed. This rapid heat dissipation precludes adequate identification of hot spots in a particular thermal image.
As an alternative to imaging cool components by opening the cabinet door, the thermography industry has placed fixed IR transmitting windows in a panel or door of high voltage electrical cabinets. These windows can provide a line of sight within the cabinet so that it may be inspected without being opened while the components within are energized. However, the view into the cabinet is limited through a single fixed window which usually cannot provide a view of all components or areas to be inspected. Some vendors have proposed the installation of multiple windows in a single cabinet, but this approach can be expensive to implement and inefficient for a thermographer having to maneuver to inspect the cabinet at each window location.
Others have addressed the limited view problem by adding an expensive wide angle lens to the inspection camera in addition to the fixed window or a small open portal. Such a lens may provide an increased field of view within a cabinet, but it also requires the user to exchange lenses to switch between this application and other thermography applications where a narrower field of view is preferred. Moreover in many cabinet applications, it is desirable to use a standard field of view camera because such a camera provides higher spatial resolution images of devices in the cabinet.